1. Field of the Invention
This invention relates in general to computer systems and more particularly to an apparatus and method for generating the various types of character sets including multiple national language character sets.
2. Description of the Prior Art
The character generator is the means for translating from the character code associated with a particular character to be displayed on a cathode ray tube to the dot pattern for that particular character. In order to achieve suitable speeds, character generators are usually implemented in hardware using a table look-up scheme with a table stored in a dedicated memory, usually a ROM/PROM with the character code serving as a portion of the address to the memory. There are various methods for character generation.
An overview of the technology of receiving digital coded data and displaying it in decoded form on a cathode ray tube is presented in the decision of the court in RCA Corp V. Applied Digital Data Systems Inc., 217 U.S.P.Q. 421 (D.C. Del 1983). One type of system stores character codes for a display, and those codes are applied through a character generator to generate the video bits to be applied to the CRT with each raster scan.
The advantage of the raster scan technique of generating characters by digital techniques comes into play only if one can operate at speeds at least equal to commercial or entertainment TV rates. This requirement is met in the prior art by utilizing ROM/PROMs to achieve the speed. This technique has the limitation of requiring a dedicated memory for character generation, thus only one character set can be generated and additional character sets including different formats such as elite and pica and also foreign characters require additional hardware in the form of hardware in ROMs/PROMs. This necessitates that the manufacturer store a variety of these pieces of hardware in order to provide full service to customers throughout the world.
What is needed, therefore, is a character generator that is loadable rather than fixed (ROM/PROM) so that multiple character sets can be provided with a single hardware configuration.